mark the upper side of the thorax with a straw dipped in the coloured
glue. The insect is not disturbed by that slight touch. It flies off;
it returns laden with mortar or pollen. You allow these trips to be
repeated until the mark on the thorax is quite dry, which soon happens
in the hot sun necessary to the Bee's labours. The next thing is to
catch her and imprison her in a paper bag, still without touching her.
Nothing could be easier. You place a small test-tube over the Bee
engrossed in her work; the insect, on leaving, rushes into it and is
thence transferred to the paper bag, which is forthwith closed and
placed in the tin box that will serve as a conveyance for the whole
party. When releasing the Bees, all you have to do is open the bags.
The whole performance is thus effected without once giving that
distressing squeeze of the fingers.

Another question remains to be solved before we go further. What time-
limit shall I allow for this census of the Bees that return to the
nest? Let me explain what I mean. The dot which I have made in the
middle of the thorax with a touch of my sticky straw is not very
permanent: it merely adheres to the hairs. At the same time, it would
have been no more lasting if I had held the insect in my fingers. Now
the Bee often brushes her back: she dusts it each time she leaves the
galleries; besides, she is always rubbing her coat against the walls
of the cell, which she has to enter and to leave each time that she
brings honey. A Mason-bee, so smartly dressed at the start, at the end
of her work is in rags; her fur is all worn bare and as tattered as a
mechanic's overall.

Furthermore, in bad weather, the Mason-bee of the Walls spends the
days and nights in one of the cells of her dome, suspended head
downwards. The Mason-bee of the Sheds, as long as there are vacant